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Question about knob and tube wiring

J

joe

Jan 1, 1970
0
Some of the wiring in our house is knob and tube. We run small loads on it
all the time - a few lights, and I would like to run a space heater, about
1000 watts.

Do you think there will be any problem with running something like that?

The circuit is hooked into the circuit-breaker panel, along with all the
other wiring.
 
R

RW Salnick

Jan 1, 1970
0
joe brought forth on stone tablets:
Some of the wiring in our house is knob and tube. We run small loads on it
all the time - a few lights, and I would like to run a space heater, about
1000 watts.

Do you think there will be any problem with running something like that?

The circuit is hooked into the circuit-breaker panel, along with all the
other wiring.

1000 watts does not constitute a "small" load. The wires themselves
will probably be ok, but look carefully at *all* connections. Any
looseness, evidence of overheating (discoloration, burnt insulation,
etc) tells you that it is time to replace the old wiring with modern
stuff. In fact, it is time regardless.

bob
 
V

Vaughn Simon

Jan 1, 1970
0
joe said:
Some of the wiring in our house is knob and tube. We run small loads on it
all the time - a few lights, and I would like to run a space heater, about
1000 watts.

Do you think there will be any problem with running something like that?

The good In theory, there is nothing wrong with knob & tube wiring. It
is a perfectly safe wiring method.

The bad Your wiring is probably at least 40 or 50 years old, and that is
where the potential problems come in. Nobody here can answer your question
because we can't see your wiring. We have no idea what the ravages of age have
done to your wiring system, or what half-assed modifications or repairs may have
been done by others over previous decades.

My daughter's house is an example, a 40's house with some knob & tube. Loose
fill Insulation has been added in the attic at some point in the last 50 years,
so the conductors are no longer in open air for cooling. The insulation on the
cables that lead to the electrical boxes is old and crumbling. We only use that
old wiring for small loads like lighting, and are replacing it as the
opportunity presents itself. In that particular home, I would never connect a
heater or other heavy load through that old wiring. YMMV.

Vaughn
 
C

clare at snyder.on.ca

Jan 1, 1970
0
OK, since I'm obviously the only one who doesn't know; what is knob and
=tube= wiring?

Knob and tube wiring is named after the insulators used to run the
wires. The wire goes THROUGH beams, joists, and rafters etc in
ceramic tube insulators, and runs ALONG joists, studs, etc. on ceramic
"knob" insulators. The wires are single conductor solid copper with
fabric covered rubber insulation. Generally houses wired with knob and
tube used only a few circuits, and often they were "ring" circuits. A
pair of wires would run basically around the house, or a portion of
it, with "drops" to lights and plugs. Initially wall switches were
uncommon - only installed in "upper class" residences, and generally
they were "drop circuits".
 
P

PhattyMo

Jan 1, 1970
0
Bob said:
Make sure that NONE of the K&T has had insulation put over or around it. A few
lights and 1000 watts is going to be pretty close to the maximum designed load.
Then hope that all the connections are still good. Personally, I'd run a new
wire.

I replaced a 14/2 wire to my bedroom with a 12/2. The output of my 1500 watt
heater seemed like it doubled. So, a lot of heat was being lost in the old wire.

Bob

Yes,heating up the inside of your walls! and possibly the contacts on
the outlet.. That's how electrical fires start,Ack!

I'm probably over paranoid,but I'd replace all the knob and tube stuff
F'n *ASAP*. I wouldn't trust it to run a 100W light bulb.

Even newer houses,with 'modern' wiring can make me nervous.
Like how the lights in the bedroom all dim when my GF uses her
hair-dryer. I'm seriously half tempted to run a dedicated circuit for
it. It just makes me nervous.
One of the houses she was looking at buying had oolldd wiring in it,and
someone had spliced in some half-assed runs of Romex at some point.

"So,How do you like it?"
"It's nice,but it's going to need to be completely re-wired before you
plug in as much as a night-light."
 
J

joe

Jan 1, 1970
0
Thanks to all who replied. It sounds like it's best to play it safe and
continue to use the circuit only for 'light' work.
 
B

Bob the Tomato

Jan 1, 1970
0
Hey Bob,
I may be FUBAR, but I bought some 12-2 to extend a very small circuit
and found after it had been run in a tortuous fashion (you don't wanna know)
that I was hooking to to 14-2. It's just for a pair of cfls and a computer;
am I asking for trouble?
Thanks for any help you can give,
Jim


If you have an existing 14-2 circuit, the breaker will be 15A. You
can add *larger* wire, i.e. 12-2, but not smaller wire.

12-2 wire would be meant to carry 20A. It won't hurt anything to put
in larger wire in this instance.

Going the other way is a common problem, and it's a violation of NEC
code. If you start with a 20A circuit and 12-2 wire - say you wanted
to add a single outlet to the end of the circuit that would only be
used to run something small like a fluorescent lamp drawing 1 amp.
It's pretty common, unfortunately, for the uninformed weekend warrior
to put in 14-2 wire... since it's only drawing an amp, right?

The problem is that the smaller wire becomes the fuse. In the event
of an overcurrent draw on that last outlet (say someone plugged in a
toaster and a hair dryer instead) the wire would melt inside the wall
instead of safely popping the 20A breaker. (Yeah, yeah, I know that
there is a little safety factor built into the Code, but that is the
basic idea.)

SO to make a long story short, you can use wire that is too big, but
never use wire that is too small.
 
B

Bob the Tomato

Jan 1, 1970
0
Yes,heating up the inside of your walls! and possibly the contacts on
the outlet.. That's how electrical fires start,Ack!

I'm probably over paranoid,but I'd replace all the knob and tube stuff
F'n *ASAP*. I wouldn't trust it to run a 100W light bulb.

Even newer houses,with 'modern' wiring can make me nervous.
Like how the lights in the bedroom all dim when my GF uses her
hair-dryer. I'm seriously half tempted to run a dedicated circuit for
it. It just makes me nervous.
One of the houses she was looking at buying had oolldd wiring in it,and
someone had spliced in some half-assed runs of Romex at some point.

"So,How do you like it?"
"It's nice,but it's going to need to be completely re-wired before you
plug in as much as a night-light."


Old knob and tube wiring, as another wrote, was probably safe at the
time. The addition of loose fill insulation and adding Romex splices
would scare the bejeezus out of me. I wouldn't sleep there.

One of the first questions you are asked when you sign up for
homeowner's insurance: "Is there *any* knob and tube wiring in the
house?"

I found a short run of remaining K&T that was still running a couple
of lights while I was up in the attic fixing something else. The
project came to a screeching halt and I ripped it out right then and
there and replaced it.

A couple of things from your post:
I had a girlfriend running a space heater on a flimsy lamp cord type
extension. It was very hot to the touch! And the vinyl coating had
that "wet" look. I figured it probably was a couple of hours away
from a fire when I caught it. Yikes!

The bathroom and hair dryer incident that you mention above:
A bathroom should have a 20A circuit near the bathroom counter for
hair dryers, etc. It is required to be GFCI, to prevent you from
getting shocked. (Google this if you don't know what it is.) That
circuit should be separate from anything else. The bathroom lights
and fan should be on a different circuit so they don't dim out when
you turn on a big load. Run 12-2 wire to for the circuit to the
bathroom counter.
 
C

clare at snyder.on.ca

Jan 1, 1970
0
Thanks Clarence,
I did a full re-wire on a house built in 1934 replacing 2 conductor
cable wrapped in braided cotton sleeves and then rolled in tar and mica.
That must have been a =new= thing in '34!

ROMEX was just starting to be used about then. MISERABLE, DIRTY crap
to work with!!!!!!

General Cable invented ROMEX in 1922 - named after the plant where it
was made in ROME New York.
It came into WIDE use after the war, but saw limitted use in the mid
thirties in some areas.
 
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